System responsive to failure of receivers



H. T. WINCHEL 2,508,983

SYSTEM RESPONSIVE T0 FAILURE OF RECEIVERS May 23, 1950 Filed Sept. 17, 1946 POWER SUPPLY l AUXILIAR RECEIVER DETECTED OUTPUT INVENTOR HENRY T. WINCHEL ATTORNEY F'atented May 23; 1950 SYSTEM RESPONSIVE TO FAILURE OF RECEIVERS Henry T. Winchel, Los Angeles, Calif., asslgnor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application September 17, 1946, Serial No. 697,461

4 Claims. 1

This invention relates broadly to high frequency receivers having automatic volume control. It is most frequently applicable to radio receivers although it is also useful in systems for the reception of waves guided by wires and the like.

In some high frequency communication systems, receivers must be receptive to signals at all times even though long periods may elapse between successive signals. One example of a system of this type is an alarm system employing radio communication links for the transmission of alarm signals. In such systems many days may elapse between the transmission of successive alarm signals yet the receiver must be capable of receiving a signal whenever it is transmitted.

An object of the invention is to provide a reliable and practicable method and apparatus for detecting failure of a high frequency receiver.

Other more specific objects and features of the invention will become apparent from the following description of a particular embodiment of the invention as illustrated in the single figure of the drawing.

Thus referring to the drawing, there is shown a main receiver II] having an associated antenna II and an audio output lead I2. The receiver I is of the type having automatic volume control in which the sensitivity "is decreased automatically in response to the reception of signals, the reduction in sensitivity being effected by the application of an increased negative bias to the grids of some of the tubes in the receiver. The particular circuits that may be employed are well known and for that reason are not illustrated in the schematic drawing. Suffice it to say, the automatic volume control voltage is brought out from the receiver III on a conductor I3.

The main receiver II] is shown as energized from a power supply I6 which is normally connected to the main receiver I0 over the armature I1 and back contact I8 of a relay I9. However, when the relay I9 is actuated, the power supply I6 is disconnected from the main receiver I0 and is connected to an auxiliary receiver I over the value.

2|b (which is grounded) through a tapped resistor 23. The upper portion 23a of resistor 23 is connected across two diagonal points of a bridge rectifier 24, the other two diagonal points of which are connected between the audio output conductor I2 and ground through condensers 26 and 28. The tap 23.0 on the resistor 23 is also connected to the AVG conductor I3. A resistor 21 may be shunted across the bridge rectifier between the condensers 26 and 28 to stabilize the circuit.

' Normally when the receiver I0 is not receiving a signal it is automatically adjusted into a condition of extreme sensitivity by reduction of negative potential on the AVG conductor I3 to a low Hence this potential when applied to the tap of the resistor 23 would not be effective to bias the tube 2| to cut-off. However, under such conditions there is a substantial A. C. noise potential on the audio conductor I2 when the receiver I0 is functioning properly, and this noise potential when rectified by the bridge rectifier 24 develops an C. potential across the upper section of the resistor 23 which biases the tube 2| to cut-off. Hence as long as no signal is being received and the receiver Ill is functioning properly, it is adjusted to a condition of extreme sensitivity in which substantial noise currents are developed and the potential of these noise currents on the conductor I2 is sufficient to bias the tube 2| to cut-off.

When a signal carrier wave is received on the antenna II and applied to the receiver ll] the AVG system of the receiver is actuated to reduce the sensitivity. Hence in the absence of a modulation on the received wave there would then be no noise potential on the conductor I2 to bias the tube 2| to cut-off. However under such conditions the negative potential on the AVG conductor I3 is sufiicient to bias the tube 2| to cut-ofi.

It will be apparent therefore that so long as the receiver I0 is functioning properly the tube 2| will be biased to cut-oil irrespective of whether no signals are being received or whether a modulated or unmodulated signal wave is being received. However in the event receiver I0 fails to function, or loses its normal sensitivity from gradual deterioration, it will then cease to apply either the noise potential to conductor l2 or the AVG potential to conductor I3 necessary to bias the tube 2| to cut-oil, and the latter will become conductive to energize the relay I9 and pull the armature II to energize the auxiliary receiver I5.

It will be understood that in practice the auxiliary receiver I5 may have its audio output conductor 25 connected to the same audio receiving apparatus that the audio conductor l2 of the main receiver is connected to. Furthermore the energization of the auxiliary receiver may be from a separate power supply instead of from the power supply IS.

The essence of the present, invention is not in the particular switching arrangement for energizing an auxiliary receiver, but in the circuit for energizing a device such as the relay 19 only in response to failure of the main receiver. For instance, the invention might be employed to'mere- 1y sound an alarm and thereby direct the attention of an attendant to the fact that the receiver has failed. I The tube 2| may be of various types and may have other electrodes in addition to the cathode,

grid and anode as shown. Furthermore it may be of the high vacuum type or may be of the gasfilled type.

As shown in the drawing, the anode 2 lo of the tube 2! is energized by a battery 26 but '=othe'r sources of potential maybe employed, eitherAC. or D. C. It is often convenient and desirable to employ a gas-filled tube of the thyratron type as the 'tube2'l and employ an A. Crpower source as the source 26.

Although for the .purpose of explaining the invention a particular embodiment thereof has been explained in detail, various departures from the particular circuit shown can be made without departing from the invention as defined in the appended claims.

I claim:

1. In a high frequency signal receiving system adapted to receive a signal-modulated carrier: carrier Wave receiving and detecting means of variable sensitivity including automatic volume control means generating a first unidirectional potential in excess of a predetermined value in response to reception of a carrier wave, and ineluding an output circuit to which detected alternating potential signals are applied; means connected to said output circuit io'r generating :a second unidirectional potential proportional to the strength of a-lternatingpotentialsin said out- ;put circuit, said receiving means normally being of such sensitivity that said second potential 1 exneeds said predetermined value :in response to :re-

in response to simultaneous reduction of both said unidirectional potentials below said predetermined level. v Y

2. Apparatus as described in claim 1 in whioh said actuating means comprises: an electric dis- 7 charge tube having a control grid and being of such characteristics that it is capable of being rendered non-conductive in response to a :potential on said grid less than saidpredeterm'ined value; means responsive to a change of said tube from non-conductive to conductive condition; and means for combining said two unidirectional potentials and applying the resultant potential to said grid.

3. Apparatus as described in claim 1 in which said actuating means comprises: an electric dis charge tube having a control grid and being of such characteristics that it is capable of being rendered non-conductive in response to a potential 'on said grid less than said predetermined value; a pair of resistor elements connected in series between the cathode and the control grid of said tube; means for applying said first potential to the juncture of said two resistor elements, and means for applying said second potential between said junction and said grid.

4. In a high frequency signal-receiving system for reception of an intermittent signal-modulated carrier wave: carrier wave receiving and detecting means of variable sensitivity including an automati'c volume control circuit the unidirectional potential of which increases with the strength of signals applied to said receiving means, and including an output circuit to which detected-signals are applied, said receiving means normally being of such sensitivity as to develop substantial noise potentials in said output circuit in the absence of a received carrier wave; an electric discharge tube having input terminals and output terminals and capable of rendering its output terminals conductive in response to a deduction in potential between its input terminals below a predetermined value; means in the output circuit of said tube responsive to a change of said tube from non-conductive to conductive condition; apair of resistor elements connected in series across the input circuit of said tube; means connecting said automatic volume control circuit across one of said resistor elements; a rectifier having a pair of alternating current input terminals and. a pair of direct current output terminals; means coupling said output circuit of said receiving and detecting means to said input terminals of said rectifier for the application thereto of alternating potentials in said-outputci-rcuit of said receiving and detecting means while isolating said input terminals from said receiving and detecting means with respect to unidirectional potentials; and means connecting the out-- put terminals of said rectifier across the-other of -S'a-id resistor elements, said automatic volume control circuit and said output terminals of said rectifier being so poled as to cumulatively apply the automatic volume control potential and the rectified detected currents to the input circuit of said discharge tube.

HENRY T. WINCHEL.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,156,809 Fredrickson May -2, 1939 2,252,218 Andrews Nov. 11, 1941 2,367,327 Beers Jan. 16, 1945 2,367,378 Schick n. Jan. 16, 1945 2,426,580 OBrien Aug. 26, 1947 

